Primary cell



W. R. FORSYTHE Nov. 10, 1942.

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` IN V EN TOR. y \V/`///'am Fonsy//a e ATTo/LNEYS Patented Nov. l0, 1942 PRIMARY CELL z William R. Forsythe, Midland, Mich., assig'nor to' The Dow Chemical Company, Midland, Mich.,

a corporation of Michigan y Application .my s, 194.1,v serial Nt.V 401,435

claims. (ci. iss-10o) This invention relates to an improved primary cell utilizing metallic magnesium as the anode material.

An object of the invention is to provide a primary cell which is capable of a considerably higher energy output per unit weight than cells now in common use. Another object is to provide a .cell which is of unusually simple construction and m-ay be readily fabricated from a very few elements. A further 'Objectis' to prodoes not deteriorate when standing without delivering current. Other objects will be evident from the description.

.The essential elements of the new primary cell are an anode composed of metallic magnesium, a cathode of chemically inert electrically conducting material such asv carbon or graphite, and an electrolyte invcontact vwith the electrodes and consisting essentially of an aqueous solution of chromic acid.

The anode may be formed either of pure metallic magnesium or of a magnesium-base alloy containing a major proportion of the metal, all such materials being included with the term magnesium as hereinafter"employed,l However, metallic magnesium of at least 99.5 per cent purity is to be preferred because of its somewhat higher electrode efficiency and its higher hydrogen overvoltage. I.

The electrolyte.v preferably consists 'offa Water V solution of chromic acid,.' and is'. conveniently prepared by dissolving chromic anhydride (CrOs) in distilled Water. Concentrations of ichromic anhydride of from 11 parts by weight per `100 Fig. 1 is a diagrammatic vertical section of a simple form of the new cell; and

Fig. 2 is a similar section of another form of the cell.

.The cell illustrated in Fig. 1 is contained in a j ar 3 of an insulating substance such as glass or molded synthetic plastic, fitted with a tight cover 4 of like material, and filled with a water l solution of chromic acid 5.. ,Depending into the ,10'- vide a cellwhich is not subject to gassing and parts of water up to a saturating amount are,

preferred. This electrolyte is inert to the magnesium anode except when the cell is delivering current, and even then does not cause the for-'- mation of any significant coating on the electrode.

Small proportions of inert solu-tes may, of course, be present in the electrolyte without departing from the invention. In general, however, a simple water solution of chromic acid is jarfthroughseparate hole'slin the cover so as to contact the y'electrolyte are a magnesium rod 6 and a carbon rod 1, each rod being provided with 'a binding post.

The cell of Fig. 2,' which is of the dry cell" type, i-s contained in a cup 8, formed doi metallic magnesium, 'the cup alsoserving as the anode of the cell, and-being for this purpose provided with abinding post 9. Fitting closely inside the magnesium.' cup is a liner I0 separating the anode from the'cathode 'portion of theA cell, the liner being formed of a chemicallyv inert electrically non-conducting porous material such as blotting paper', cloth fabric, or .the like. Inside the liner the cell is iilledwith a mass of nely-divided carbon H, Withwhich a carbon rod I2 extending through the Asealed insulating cover I3 is in direct electrical contact. 'Ihe mass of fine carbn issaturated with a water solution of chromic acid as electrolyte.

,. 'The' electrolytic reaction in the new cell is not .fully understood, but appears to involve an oxi-` dation atrrtheanod'e of the metallic magnesium, vprobably with the formation of magnesium chromate, and aj reduction as the cathode of the chromic acid, with liberation of trl-valent chro.

mium salts.

The cell develops an open circuit potential of l about 1.2.vol-ts, while the energy output per unit fweight of cell is considerably in excess of that solution of chromic acid.

2. A primary ycell `comprising a magnesium anode. a'carbon cathode, and-an electrolyte coni-)istinti` oi' a water solution of chromic acid.

3. A cell according to claim 2 wherein the metallic magnesium forming the anode is of at least 99.5 per cent purity. v

4. A primary cell in whlch'the essential elements consist of a magnesium g anode, a carbon 5 cathode. and an electrolyteconsisting of the solution prepared by dissolving at least 11 parts by weight of chromic anhydride in I100 parts ot wa ter. 

